Comparison of culture methods for the detection of Salmonella in wastewater

Abstract

The goal of this work was to find an effective culture method for the detection of Salmonella in wastewater, which would consider both the recommendation of ISO standard 19250 and the specific nature of the wastewater matrix. Three culture methods that differed primarily from the use of the non-selective pre-enrichment step and the processing of wastewater samples prior o the selective enrichment step and further divided into ten protocols depending on the selective enrichment conditions, have been compared with respect to the detection of Salmonella in naturally polluted municipal and hospital wastewater samples. Two selective enrichment broths (MKTTn and RVS) at two incubation temperatures (37 °C and 41.5 °C) plus four media (XLD, DC, BG, and Rambach) were used in this study. The results have shown that the selective enrichment step is the key factor in the culture protocol for detecting Salmonella in wastewater. Such conditions for enrichment (that is, the broth and incubation temperature used) had a major effect on the multiplication of Salmonella to detectable levels, suppressing competing bacteria, and on the efficiency of solid media, thus significantly influencing the isolation rates of Salmonella from wastewater. MKTTn broth performed better for Salmonella isolation from wastewater than that for RVS broth. Incubation at 41.5°C significantly increased the level of Salmonella detection by both selective enrichment broths. XLD and DC agar were the most efficient solid media in this study. The combination of MKTTn broth incubated at 41.5 °C and XLD agar constituted the best approach for isolating Salmonella from wastewater.